1. Field of the Invention
The present invention relates to a micro pattern forming method for a semiconductor device, and more particularly, to a gas mixture used in etching an electrode layer made of polysilicon, and to an etching method using the gas mixture.
2. Description of the Related Art
Polysilicon is generally used as the conductive material of choice for forming a lower electrode of a capacitor during the process of manufacturing a semiconductor device. In order to form an electrode, a layer of polysilicon is first deposited on the semiconductor substrate. A mask pattern is then formed over the polysilicon layer. Finally, the polysilicon layer is etched using the mask pattern as an etching mask.
To pattern the polysilicon electrode layer, etching methods using a plasma are typically employed. An etching apparatus employing TCP (Transformer Coupled Plasma) technology can form a sufficiently uniform plasma by creating an electromagnetic field using a coil shaped conductor or similar structure. The TCP etching method anisotropically etches the polysilicon electrode layer by directly controlling an ion density or an upper power source, to obtain selectivity of the etching gas for oxide and photoresist materials.
Conventionally, when forming an electrode layer made of polysilicon, a gas mixture containing mostly hydrogen bromide (HBr) is used as an etching gas. The HBr gas has a strong tendency to etch the polysilicon electrode layer vertically, which protects the side walls of the etched layer during the etching process. HBr is also highly selective for etching the oxide layer used as the mask layer. One disadvantage of using HBr gas in the etching gas mixture, however, is that it results in a low etch rate which makes the etching process less reproducible and results in inferior products. HBr gas also results in the overproduction of unwanted byproducts, such as polymers, which generate contamination and create a need for frequent regular cleaning of the etching apparatus.
Therefore, a need exists for an etching gas mixture that can efficiently etch a polysilicon electrode layer without generating unwanted, contaminating byproducts. The etching gas mixture and the method of etching an electrode layer of the present invention reduce etching time, reduce contaminating byproducts and enhance reproducibility.